It would be illegal for me to take these rifles over 12ftlb so in .22 that would be around 610fps with a 14.5grain pellet or 800fps with an 8.4 grain pellet in .177
I could go over these but I'd need to apply for a Firearms Certificate and be limited as to where I used them.
Sure I'd be interested in seeing what you have.

more of a people apocalypse, y'know, when the population goes rabid because of a conspiracy where people under obamacare are vaccinated against a gov't created microbe and everyone else is not and they release it on their own citizens to cause widespread panic and kill off everyone who isn't a supporter... or something like that anyways

I got my first .410 for my 14th birthday it had a 28" O/U barrel and folded up double to fit in my pocket (although I had to wear a scarf to hide the top of the barrel when walking to the shooting grounds.

Largest wild animals around here are Red Deer and Roe Deer but they're not for shooting. The largest predator in the UK is a Badger followed by Fox. Badgers can't be shot but foxes are fair game but I wouldn't take one with an airgun.
It's a long time since bears and wolves walked these shores but there is a nutter up in Scotland that wants to bring them back, after all he's been quite successful with the reintroduction of beavers